The present invention is directed to communication distribution networks, and especially to communication loop frequency utilization in such networks.
During setting up, or “training” line cards in a channel bank for distributing operating frequencies among communication loops coupled with the channel bank, respective line drivers and their coupled communication lines are traditionally addressed in a serial fashion. That is, once a given line is trained, a second line is trained and so on. Each time a line is trained it involves an allocation of a plurality of tone-sets, or frequency-sets, used by the particular line card in communicating with subscriber equipment (also known as Customer Provided Equipment or Customer Premises Equipment—CPE). Line training involves establishing synchrony with CPE (customer premises equipment or customer provided equipment) at the distal end of the line from the central office, and applying an algorithm or other test to achieve an acceptable data rate under a given set of criteria. Certain tones may not be used by the system for a particular line if the signal-to-noise ratio (SNR) is unacceptably low for them. To remedy an unacceptably low SNR, a system may, for example, assign fewer bits to a particular tone.
Each successive training process accounts for noise present on the line being trained at the time the training is carried out. As more lines are added to a channel bank, more noise is present. This occurs because there is necessarily progressively more cross talk among lines as lines are added. Additional noise is also present because adding more lines also adds more noise sources to the system, for example from additional CPE or from additional environmental noise sources. Each successive line is trained to achieve the highest number of bits per frequency or tone that can be sustained while maintaining acceptable signal margin. That is, each line is trained to its highest sustainable bit error rate (BER) under the circumstances that are extant during the training process.
After the last line card in a channel bank is installed and trained, the first-installed card experiences more noise than was extant when the first card trained up. There are commonly 75 to 80 line cards to a channel bank, and each line card typically is coupled to support one to four lines. The result is that first-trained lines may find it difficult to communicate, using the parameters that were set during their respective training processes, without incurring symbol errors.
The term symbol has a very specific meaning in an ADSL context. For example, if one is using 100 tone pairs, each of which is carrying 10 bits. 1000 bits are distributed among the 100 tone pairs to comprise a symbol that is sent for a symbol period. 1000 bits are being transmitted in the symbol.
One solution has been to effect a “reinstallation” process after all line cards are installed and trained. In carrying out such a process, an installer physically pulls out each line card and restarts each line card to allow the coupled lines to retrain. This process can take up to one minute per line card so that the entire “reprogramming” process can take more than an hour.
There is a need for a method for allocating operating frequencies to communication loops that provides an allowance for noise that will exist when all lines for a system are installed.